Printing devices, such as inkjet printers, can produce an image on a recording medium (e.g., paper) by forming an image layer on an image receptor, transferring the image layer to the recording medium, and fusing the transferred image to the recording medium. In some processes, the transfer and fusion steps are contemporaneously performed (hereinafter referred to as “transfusing” or “transfixing”). The locus of contact is commonly referred to as the nip.
Using solid-ink compositions currently available in the industry, transfer of the image layer from the image receptor (in the form of a belt or drum) to the recording medium is generally accomplished by contacting the image layer with the recording medium under pressure and, if desired, heat. Transfixing pressure is typically provided in the nip by a roller selectively biased against the recording medium. High-speed printers generally require controlled high pressures, generally in the range of about 550 pounds per square inch (approximately 250 kg/in2) to more than 2000 psi (approx. 900 kg/in2) depending on the particular solid ink compositions employed, the size of the recording medium, desired print quality (e.g., draft, final), applied heat, and the like.
Transfix roller load heretofore has been controlled by one or more pre-tensioned springs. A motor or other retracting means is utilized to retract the roller from the nip or to extend the roller into the nip, against the tension of the spring(s). The spring tension may be created by either of compression or extension of the spring from its resting state.
Springs generally deliver a slightly fluctuating roller load depending on variations in paper, device component run-out and the like. To provide effective pressure delivery, printing device manufacturers have produced devices having precise and minimal run-out of the transfixing roller and the image receptor drum, employed innovative ink compositions to control image layer thickness, viscosity and transfer properties, and urged use of consistent recording media.
As well, printing devices with tensioned springs generally require more complicated manufacturing processes and add bulk to the finished product. Highly tensioned spring elements within a printing device chassis may potentially be dangerous to assembly and/or repair personnel.
It would be desirable to provide transfix roller load without use of tensioned, high-strength springs. Further desirable is the capacity to vary the load force based on image content and print mode. If text only prints could run at reduced load, for example, roller life would increase and power consumption would decrease.